ajN'imal to its shell in some fossil cephalopoda. 109 



length of the hody-chamher, hut I venture to helieve that it will prove to ha clue to 

 other causes, and also affoi'd an important character for the purposes of classification. 

 Thus, among the forms of muscular attachment descrihcd in the present paper, the 

 shell-muscles in Distichoceras and Oi^peUa seem to have been relatively much longer 

 than those of the other forms herein described ; and hence one should expect these two 

 genera to be closely related. Tliis affinity seems to be supported by their other characters, 

 for they have been placed in the same subfamily, viz. the Oppelince*. 



Not only was the Ammonoid animal, like the Nautilus, at least at some periods, 

 attached to its shell by means of the lobes and saddles of the posterior portion of the 

 body (corresponding to those of the edge of the septum of its shell), but it seems from 

 the foregoing descriptions that it was further provided with an annulus in addition to 

 shell-muscles as in the recent Naiitilus. It would appear, therefore, as if the provision of 

 an annulus were an absolute necessity to the animal in addition to the shell-muscles, 

 and most probably Dr. Waagen's explanation of its occurrence is the correct one, viz., 

 that the annulus and shell-muscles served not merely to hold the animal to its shell, 

 but formed also an air-tight band around it, fastening the mantle to the shell. 



In conclusion, I desire to express my obligations to those who have in any way assisted 

 me in my observations. To Dr. Woodward I am greatly indebted for valuable 

 suggestions and much kind help, while to Mr. B. B. Woodward I am especially 

 indebted for the advice which he has ever been most willing to give me. My thanks 

 are also due to my colleague Mr. Edgar A. Smith for giving me every facility in the 

 examination of the recent Cephalopoda under his charge. For the loan of specimens 

 I have to thank Mr. F. L. Bradley, Mr. G. P. Harris, and the authorities of the 

 Jermyn Street Museum. To Messrs. Sharman, Newton, and Allen, of that Museum, 

 I am under deep obligations for all their kind help during the examination of the 

 specimens under their charge. To Professor Howes, whose interest in my work has 

 been a source of great encouragement to me, I desire to present my cordial thanks. 



EXPLANATION OF THE PLATES. 



The figures are of the natural size unless otherwise stated. 



X indicates tlie last septum. 



— * marks the remains of the muscular attachment. 



Plate 17. 



Baculites ovatus, Say (p. 77). 

 Fig. 1. Dorsal aspect of fragment of body-chamber, showing anterior boundaries of muscular scars. 



2. Right lateral aspect of same, showing on the left the boundary of the right muscular scar, and 

 on the right the incised line on the ventral area. 



See Prof. Dr. K. A. v. Zittel, ' Grundziige der Palaoutologie,' p. 420. 



